Microbial community composition and biofouling in a forward osmosis membrane bioreactor and a membrane distillation bioreactor

• Main Author: Zhang, Qiaoyun
• Other Authors: School of Biological Sciences
• Format: Theses and Dissertations
• Language: English
• Published: 2014
• Subjects: DRNTU::Science
• Online Access: http://hdl.handle.net/10356/61538
• Institution: Nanyang Technological University

The forward osmosis membrane bioreactor (FOMBR) and the membrane distillation bioreactor (MDBR) are two high retention membrane bioreactors (HRMBRs) which allow efficient separation of colloidal and dissolved matters from wastewater, which in turn results in salt accumulation in the bioreactor. These reactors provide a novel environment for resident microorganisms that play a crucial role in the degradation of pollutants. Membrane biofouling is a major problem for conventional membrane bioreactors (MBRs). However, the propensity for membrane fouling in FO and MDBRs is unknown. Therefore, this study aimed to characterize the microbial community and membrane fouling in an FOMBR and in an MDBR system. The FOMBR was run for four times with different operating parameters, lasting for 73, 35, 35 and 43 days respectively. A submerged MDBR was operated at 55 ℃ for 105 days at a pH of 10, followed by 102 days at a pH of 8. Molecular technologies were employed to characterize the bacterial communities. Bacterial communities were characterized using denaturing gradient gel electrophoresis (DGGE) and 16S rDNA pyrosequencing while the archaeal and eukaryotic communities were analyzed using 16S and 18S rDNA pyrosequencing. A well-established biostatistical analysis pipeline was selected to analyze the sequencing datasets. Confocal laser scanning microscopy (CLSM) and image analysis were used for the visualization and characterization of membrane biofouling. Pyrosequencing revealed rich and diverse bacterial communities in the suspended sludge of the FOMBR, with only 4 genera of archaea detected in the last run. Both the bacterial and eukaryotic communities changed over time and changes in community composition correlated with different operational parameters. Fungi dominated the eukaryotic community, and the pattern of non-metric multidimensional scaling (NMDS) plots of eukaryotic community samples was different from that of the bacterial community. Multivariate analysis indicated that salinity was not the primary factor that exerted an influence on the shifts in microbial communities in the FOMBR. Flux was detected to decline dramatically under low aeration operation conditions, and serious biofouling was indicated by CLSM image analysis. The composition of the bacterial communitites in the suspended sludge and the sessile biomass on the membrane surface as assessed by NMDS was significantly different under high aeration but was more similar under low aeration. The genus Pseudomonas contributed most to the dissimilarity between the suspended sludge and biofilm communities under high aeration, while Chloroacidobacterium, Terrimonas and Lactococcus contributed to the dissimilarity under the low aeration conditions. In the MDBR, bacterial communities had a relatively low richness and diversity and were abundant in Rubrobacter and Caldalkalibacillus. The conductivity, total nitrogen (TN) and bound EPS were strongly correlated with the shift in biological communities. Interestingly, no archaea were detected in the MDBR. Eukaryotic communities had a relatively high richness and diversity, and their shift correlated closely with bound EPS concentrations. Both flux profiles and CLSM images showed serious biofouling on MD membranes, where Hydrogenophaga was enriched compared to its occurrence in the sludge. Overall, our study provides novel information on the characterization of bacterial, archaeal and eukaryotic communities in an FO and MDBR operating under a variety of conditions. The characterization of the propensity for these novel wastewater treatment technologies towards membrane biofouling is fundamental for the development of efficient wastewater treatment strategies.